InUnclaimed, the much-hyped new documentary by Canadian director Michael Jorgensen, filmmakers follow a 76-year-old man discovered in the Vietnamese jungle who claims to be a former Green Beret pining for his American family.

In the movie, Mr. Jorgenson— the film’s Alberta-born, Emmy-award-winning director, who has previously led film expeditions to dig up the grave of the Mad Trapper of Rat River and examine the mysterious wreckage of a crashed nuclear bomber in the B.C. interior — explores the story of Master Sgt. John Hartley Robertson, a Green Beret whose helicopter was shot down over Laos in 1968.

After its much-vaunted premiere at Toronto’s Hot Docs festival on Tuesday, the film is set for its U.S. debut this Sunday at the G.I. Film Festival, a Washington, D.C.-based festival themed around the portrayal of American service members.

But, according to U.S. authorities, the film’s producers — and the American woman who tearfully adopted the man as her long-lost brother — have simply been taken in by a well-known Vietnamese con man.

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In response, the film-makers, whose movie hints at a government coverup in the mystery, note that the story they’re telling is that of Vietnam veteran Tom Faunce, who journeys to South Asia to meet the man claiming to be Master Sgt. Robertson.

“The film was not produced to help perpetrate fraud of any kind or misrepresent anyone’s identity, but merely follows one man’s struggle to help another,” reads a Tuesday statement on Unclaimed’s official Facebook page. The statement then directed critics to a review by Maclean’s magazine writer Brian Johnson in which he states that the film “suggests Robertson’s case is cloaked in an elaborate cover-up by the U.S. military.”

According to a recently declassified 2009 Defence Department memo, the man claiming to be Master Sgt. Robertson is actually Dang Tan Ngoc, a Vietnamese citizen of French origin with a history of making false claims to U.S. authorities.

Mr. Ngoc first approached the U.S. military with claims he was Master Sgt. Robertson in 2006. Officials said they received a purported biography in support of the claims that gave a non-existent high school and bogus U.S. home address for Master Sgt. Robertson, whose name was even rendered incorrectly.

“Most recently, in late 2008 Mr Ngoc again posed as Mr. Robertson and was taken to the U.S. embassy in Phnom Penh where he was fingerprinted,” according to a recently declassified document.

“The fingerprints were subsequently evaluated by the FBI, which concluded Mr Ngoc’s fingerprints did not match those in SFC Robertson’s records.”

My family is at peace and this is who he is. If the world doesn’t believe us, that’s fine

Mr. Ngoc, who has a wife and children in Vietnam, would have been entitled to back pay and veterans’ benefits from the American government if it had been established that he was indeed Master Sgt. Robertson.

In the film, the man claiming to be Master Sgt. Robertson cannot speak English, cannot remember the names of his American family or even many details about his American life.

Nevertheless, he purports that after being held in a North Vietnamese prison for four years, he escaped and married a Vietnamese woman, who gave him the name of her dead husband, a slain Vietnamese soldier.

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The film climaxes with a meeting in Edmonton (he is apparently not allowed into the U.S.), in which Mr. Ngoc meets Sgt. Robertson’s only surviving sister, Jean Robertson Holly, who is seen embracing Mr. Ngoc and testifying to his “true” identity in the documentary.

“There’s no question,” she says in the film. “When I held his head in my hands and looked in his eyes, there was no question that was my brother.”

Notably, the family of Master Sgt. Robertson refuses in the film to get a DNA test to ensure their blood relation, relying instead on translated testimony by Mr. Ngoc, who returned to Vietnam immediately after the Edmonton meeting.

“My family is at peace and this is who he is. If the world doesn’t believe us, that’s fine,” Robertson relative Gail Metcalf told a Toronto Star reporter at the time of the film’s premiere.

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“Ultimately, Tom’s mission ended in a family reunited with the man they have identified to be their John H. Robertson, despite the U.S. Government’s claims to the contrary,” reads a post on the film’s Facebook page.

The film’s official promotional material also hints at allegations of some sort of clandestine U.S. military conspiracy.

“Working against government forces trying to cover up the story, Tom [Faunce] struggles to prove the lost soldier’s identity and reunite him with his family,” reads Unclaimed’s website.

Liz Smith, a spokesman for the film, told The Daily Telegraph: “I can assure you that Michael performed due diligence in producing the film.”